I find the K271 to generally be boring from portable sources I've heard it with. A source with an output topology like the original iPod Shuffle would do well, I suspect (it improves a great deal through a simple push-pull buffer). While it has some details, I find it quite boring--I guess that's just how the poor amplification distortion presents itself to me. My Xin, fed w/ 12V wall power, is about my minimum for listening to it (I planned a nice amp build as part of keeping the K271 mkII, but then real life got in the way).
I also wouldn't use it portably, because it makes a lot of noise from moving. Part of what makes it comfy are the plastic parts having joints, some of it staying under spring-like tension, and the arch thingies being somewhat flexible. That also allows movement to make noise that transfers all over the headphone. For sitting down and groovin', it's no biggie (it lessens greatly with use, as well). On a bus or something, though, you'd be hearing more of the plastic crackling and groaning than you would your music.
It's a wonderful headphone, but I don't think it's good at what you want. If you were asking about using it with a real amplifier (even a receiver's HP out--I'm not talking, "high-end," just high power), for home listening, and wanted a comfortable closed headphone that sounded fairly neutral, with intimate mids, I'd say to go for it. If you didn't like it, at least you would have a better vantage point to move on from.
You aren't asking for anything remotely like that. Have you considered Audio Technica's closed models, or maybe some of the Sony ones with better reputations around here? I haven't heard them, but many are well known to sound good from any output.